1. Field of the Invention
The invention relates to Saccharomyces cerevisiae strains and processes for hyper-producing glutathione and γ-glutamylcysteine.
2. Description of the Related Art
Glutathione (GSH), a small peptide composed of L-glutamic acid, L-cysteine and glycine, is a natural anti-oxidant. It was first isolated in 1888 and formally named in 1921. Glutathione is broadly found in organisms including animals, plants and microorganisms. Its metabolism and physiological functions in animal cells, and processes for hyper-producing it are well documented (Tateishi N. et. al., 1974. J B. 75: 93-103; Issels R. et al., 1988. Biochem Pharmacol. 37: 881-888; and Meister, A. et al., 1983. Ann. Rev. Biochem. 52: 711-60). Glutathione has been used in liver protectors, scavengers of toxins and eye drops. It is also a promising ingredient of functional health food products.
The industrial processes for producing glutathione includes chemical synthesis, extraction, enzymatic production, and fermentation, among which fermentation is preferred because of its easy manipulation. Furthermore, glutathione produced by fermentation using yeasts is safer to be used in food products than the same compound produced by fermentation methods using other microorganisms, such as recombinant Escherichia coli. As a reason, yeast is widely utilized for preparing the glutathione for use in functional drinks and health food products. Yeast mutants produced by mutagens such as amide and indophenols, which improve glutathione production, have been also reported (JP60248199).
The product γ-glutamylcysteine (γ-GC) is a precursor of glutathione in the synthesis process. It is reported that γ-glutamylcysteine is effective in lowering the damage of CCl4 to the liver in a mouse. The product has functions similar to glutathione, and can regulate the glutathione content in a cell when co-exists with glutathione synthetase. In addition, γ-glutamylcysteine is an important content of human milk and can enhance immunogenesis ability of a subject.